1. Field of the Invention
This invention relates to a brake used to stop rotation of a spool of coiled wire, and particularly, to a braking system for welding machines which is economical to manufacture, provides excellent performance characteristics, and requires no factory or field adjustment over the useful life of the braking system.
2. Background Discussion
In certain welding processes, a filler material in the form of a coiled wire on a spool is fed to a welding gun. A typical welding machine which utilizes wire filler material coiled on a spool is illustrated in U. S. Pat. No. 3,562,577. In this welding machine, the wire filler material is fed by rollers carried in the welding gun to the welding site. When the welding stops, the wire feed stops essentially immediately. To prevent unspooling of the wire, it is necessary to stop the spool before it has rotated more than about twenty degrees. In existing welding machines, various brake mechanisms are employed. For example, passive friction drag mechanisms, external self-energizing drum brakes, and electromagnetic clutches are all used. These conventional brake mechanisms have various problems associated with them, such as presenting excessive loads on the wire feeder, excessive mechanical complication leading to expensive, difficult to manufacture equipment, and frequent adjustments in the field.